GREENSBORO, North Carolina (CNN) --Those familiar with an accused mastermind of the attacks of September 11, 2001 spoke Thursday about the two years he spent earning a mechanical engineering degree at North Carolina Agricultural and Technical State University in Greensboro.

Khalid Shaikh Mohammed graduated in 1986, one of about 30 Muslim students that year.

Sources said he is one of the most-sought al Qaeda leaders, after Osama bin Laden and Ayman al-Zawahiri.

"He was very helpful. The guy wouldn't mind helping ... When he talks to you, he'll be smiling," former classmate Sammy Zitawi told CNN.

One of Mohammed's professors is rattled by the revelation that he taught one of bin Laden's top lieutenants.

"I may have helped give him some background that would help him accomplish the World Trade Center catastrophe," professor David Klett said.

Records show Klett taught Mohammed thermodynamics, and Klett said he often asks himself about the course.

"We cover ... the fundamentals of jet engines and propulsion and chemical reactions, combustion reaction ... and those things would have been necessary for them to at least consider when they planned the World Trade Center attack with the airplanes," Klett told CNN.

Mohammed arrived at NCA&T in the summer of 1984. He had transferred there from Chowan College, in Murfreesboro, North Carolina.

Muslim students pro-American in mid-1980s

Zitawi said he had no inkling Mohammed held anti-American views. He said his former classmate was very religious and, if anything, he and other Muslim students were pro-American in the mid-1980s because the U.S. aided mujahedeen fighting the Soviets in Afghanistan.

"I mean, everybody was praising the U.S. for helping out the Muslims in Afghanistan, so why would anybody have anything to do against the U.S. back then?" Zitawi said.

But less than 10 years later, in 1995, Mohammed was indicted on charges of plotting to blow up commercial U.S. airliners flying to the United States from Southeast Asia. The indictment, filed in New York, remains sealed.

Investigators and other sources say Mohammed has been connected to the first World Trade Center attack, in 1993, and the bombings of U.S. Embassies in Kenya and Tanzania in 1998. He reportedly attended an al Qaeda meeting in Malaysia in 2000, where planning was done for the September 11 attacks and the bombing of the USS Cole in 2000.

Sources said he also tried but failed to use an alias to apply for a U.S. visa extension on a Saudi Arabian passport to enter the United States in summer 2001.

According to sources, he was one of three people who knew the details of the September 11 attacks and was with bin Laden when the al Qaeda leader was informed of the attacks' success.

As recently as April, German investigators linked Mohammed to the truck bombing of a synagogue in Tunisia. They said that three hours before the deadly bombing, the suspected suicide bomber telephoned Mohammed.

Authorities had hoped to find Mohammed during a raid in Pakistan on September 11 of this year, when another key al Qaeda suspect, Ramzi Binalshibh, was arrested.

Mohammed is believed to be at large in Pakistan.

The 'Forrest Gump' of al Qaeda

One U.S. official has called Mohammed the Forrest Gump of al Qaeda because of all the attacks to which he's connected. Gump was a movie character who found himself at the center of many key moments in modern U.S. history.

Klett says he can't help but wonder what was going on in Mohammed's mind during his two years at the Greensboro university.

"You wonder if at the time he was here, whether or not he was already formulating these ideas, a hatred for our country," Klett told CNN.

Mohammed's former classmate says he's astounded when he hears about all the terrorist acts attributed to the man.

"You don't know what to believe," Zitawi said, "but I think that anything is possible in this life. Years go by. People change."